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LED Tachometer Com p le t in g t h e c on s t r uc t ion & ch a n gin g t h e s e t t in gs Pt.2: By JOHN CLARKE Setting up the LED Tacho mainly involves stepping through and reprogramming the default software settings in the PIC to suit your vehicle. Here’s how it’s done. H AVING COMPLETED the PC board assemblies and made up the connecting cable as described last month, it’s now time to test the tachometer. However, before applying power, check that all parts are in their correct locations and are correctly oriented. Check also for any solder shorts between the board tracks and IC pads. Do not connect the display PC board to the main board yet – that step comes later, after the initial voltage checks. In addition, the PIC micro (IC3) should be left out of its socket. Once you are satisfied that every80  Silicon Chip thing is correct, apply power (12V DC) to the main PC board and check that pins 4 & 14 on IC3’s socket are at +5V. That done, monitor the voltage at TP1 (with respect to 0V) and check that this voltage can be varied from about 2-5V using trimpot VR1. If this checks out, switch off the power and install IC3 in its socket – see Fig.5 last month. Make sure that this IC is oriented correctly; ie, with its notched end towards the adjacent 100nF capacitor. Next, connect the display board to the main board using the IDC cable, then set VR1 fully anticlockwise and VR6 fully clockwise. Trimpots VR2, VR3, VR4 & VR5 should all be set to mid-position. Apply power and you should be greeted by a single “0” on the digital display (ie, on the righthand digit). In addition, LED1 in the bargraph should light. If this does not happen, switch off immediately and check for assembly errors (ie, parts placement, faulty or missed solder joints, solder shorts between IC pads, etc). Testing the displays Assuming everything is OK so far, you can now test the displays by switching off and then pressing the Up switch (S3) while you re-apply power. If you keep this switch pressed, the display should show all “eights”, with the two far-left decimal points also lighting. In other words, you should see 8.8.88 (do not expect the two righthand decimal points to light). siliconchip.com.au At the same time, each LED on the circular bargraph should light in sequence, followed by the shift LED when the bargraph sequence is completed. The lighting sequence should then start again. Now release the switch – the display should now show a “1” and the unit will be placed in the settings mode. To exit from this mode, simply switch off and re-apply power without pressing the Up switch. If any of the LEDs fails to light, check its orientation and the soldering. Check also for broken tracks or shorts between pads and tracks. Alternatively, the LED itself may be faulty. Operating The Tacho From 24V DC Want to operate the LED Tachometer and DC Relay Switch from 24V DC? Here’s how to do it: Tachometer • • • Change the 220W resistor feeding zener diode ZD1 to 1kW 1W Increase the voltage rating of the 100mF 16V capacitor at the input of regulator REG1 to 35V Increase the voltage rating of the 470mF 25V low-ESR capacitor following D1 to 35V DC Relay Switch • • • Use a 24V relay instead of a 12V relay – eg, the Altronics S 4208A 24V 30A relay (Jaycar do not have a 24V version). Increase the voltage rating of all capacitors to 35V. Change the 2.2kW resistor in series with LED1 to 4.7kW 0.25W. Dimming response The next step is to adjust the dimming response but first adjust VR1 so that the display is reasonably bright. You can do this using just the “0” display on the righthand digit to judge the brightness or you can use the preceding display test mode to light all the display segments. There are two sets of dimming controls and these allow you to balance the segment brightness on the 7-digit displays. This is necessary because the top and bottom segments of each display are driven by different driver ICs. Begin by adjusting VR2 and VR3 so that the top segments have the same brightness as the bottom segments. In practice, you should not need to vary these much from the previously set half-way position. Do not turn these trimpots fully anticlockwise, otherwise the dimming effect will be lost. Trimpot VR6 sets the dimming threshold – ie, the ambient light level where dimming begins. You can simulate this by placing your finger over the LDR. It’s just a matter of turning VR6 so that the displays begin to dim as the LDR is shadowed. That done, cover the LDR completely and adjust VR4 & VR5 to set the minimum display brightness. Changing the settings As mentioned, the various settings for the tachometer are changed using a special mode of operation (ie, the “settings” mode). As described above, this mode is invoked by holding down the Up switch and simultaneously applying power to the unit (if this switch siliconchip.com.au is not pressed, the tacho­meter operates in “normal” mode). Initially, the unit will go through the display test cycle just described and this is repeated for as long as the Up switch is pressed. Releasing the Up switch then causes the display to show a “1” and invokes the settings mode. The Green Mode LED will also be lit and this indicates that the display is showing the current mode selection (the default is mode 1). You can now change the mode by using the Up or Down switches to select from mode 1 through to mode 13. For each mode, you can force the display to show its current setting by pressing the Toggle switch. During this time, the Red settings LED will light and the Mode LED will be off. The settings are changed by using the Up and Down switches Basically, you have to step through and set each mode in turn. These modes and their options are as follows: Mode 1 – No. Of Cylinders: enter in the exact number of cylinders for a 4-stroke engine (1-12 cylinders). In operation, each cylinder in a 4-stroke engine fires once every two-engine revolutions. This means that a 4-cylinder 4-stroke engine delivers two pulses per revolution to the tachometer, while 6-cylinder and 8-cylinder engines respectively deliver three and four pulses per revolution. A selection of “11” (or “7”) should be made for a 2-cylinder asymmetrical 4-stroke motorcycle engine, where the firing spacings between each cylinder are uneven. This gives a steadier RPM reading compared to using the 2-cylinder option. Similarly, use a “9” setting for an asymmetrically fired 3-cylinder 4-stroke engine. Two stroke engines are also catered for. For these, simply use a cylinder number that’s double the actual number of cylinders. For example, select “2” for a 1-cylinder 2-stroke, 4 for a 2-cylinder 2-stroke, etc. Mode 2 – Red LEDs: this setting refers to the number of red LEDs used for the red line. During construction, you may choose how many red LEDs to use and these are placed at the clockwise end of the bargraph display. The number of LEDs is nominally set at “5”, however any number from 0-10 can be accommodated. Mode 3 – Red Line: this mode is used to set the maximum (or red-line) RPM recommended for your engine. The default setting is 9000 RPM but you can alter this in 100 RPM steps from 0 RPM to above 30,000 RPM. Note that this display is shown in a x1000 RPM format. So 9000 RPM will be shown as 9.00 and 10,000 RPM will be displayed as 10.00. The tachometer will light the first of the red LEDs at the red-line RPM. Mode 4 – RPM/LED: this mode shows the RPM increment for each LED in the bargraph. It is automatically recalculated when ever the number of red-line LEDs is changed (see mode 2) and when the red line RPM is changed (see mode 3). The calculation subtracts the num­ ber of red LEDs from the total of 32 November 2006  81 Table 1: Tachometer Settings Mode Possible Settings Notes 1. Cylinder Number From 1-12 Select exact number for a 4-stroke engine or use twice the cylinder number for a 2-stroke engine. Select 11 (or 7) for an asymmetrical 2-cylinder 4-stroke engine, 9 for an asymmetrical 3-cylinder 4-stroke and 6 for a 3-cylinder 2-stroke. 2. No. Of Red LEDs From 0-10 Allows changes to red-line bargraph display length. 3. Red-Line RPM From 0 to above 30,000 RPM Sets red-line RPM at first red LED. 4. RPM/LED Automatically changed No manual adjustment. Automatically adjusted with changes to Modes 2 and 3. 5. Shift Light RPM From 0 to above 30,000 RPM If not required, set RPM well above red-line RPM. 6. Limiter RPM From 0 to above 30,000 RPM Limiter output changes at limit RPM (see mode 12). 7. Hysteresis 0-255 RPM Prevents LEDs flickering on and off at threshold. Set at less than the RPM/LED value from mode 4. 8. Display Update 0-510ms in 2ms steps Sets digital display updates to a comfortable rate. 9. Display Format 0, 1, 2 1: 9999 RPM, 2: Decimal shift from 9.999 to 10.00, 3: 9.99 to 10.00. 10. Fixed Digits 0, 1, 10 Use 0 for 1 RPM resolution; 1 to fix units digit at 0 (10 RPM resolution); 10 to fix units and tens digits at 0 (100 RPM resolution). 11. Dot or Bar 0 or 1 Use 0 for dot bargraph display, 1 for continuous bargraph display. 12. Limiter Sense 0 or 1 Use 0 to set limit output normally low (0V). Use 1 to set limit output normally high (ie, +5V). 13. Limiter On Period 0-510ms in 2ms steps Sets the minimum time that the limiter output is active. LEDs used in the bargraph and divides this number into the red-line RPM. This then sets the calibration of the tachometer so that the first red LED lights at the correct red-line RPM. As a result, the number of red LEDs determines the total RPM range of the tachometer. This “RPM per LED” value is set automatically and cannot be changed manually. Mode 5 – Shift Light: this mode allows the shift-light RPM to be set. It can be altered in 100 RPM steps from the default value of 8000 RPM, over the range from zero to above 30,000 RPM. The setting is in a x1000 RPM format; eg, 8000 RPM is displayed as 8.00. Mode 6 – Limiter RPM: this mode sets the limiter RPM. In operation, the limiter output changes when the measured RPM goes above this setting and the output level depends on the sense setting (see mode 12). 82  Silicon Chip This setting can be altered in 100 RPM steps from the default of 9900 RPM over a range from zero to above 30,000 RPM. Once again, the display is in a x1000 RPM format; eg, 10,000 RPM will be displayed as 10.00. Mode 7 – Hysteresis: this setting controls the way the LEDs light in the bargraph. As the RPM increases, successively higher LEDs will light up but at the threshold RPM where a LED just lights, there will tend to be some flicker as engine RPM varies slightly (ie, the LED rapidly switches on and off). To prevent this, you can add hysteresis. The hysteresis does not affect the RPM at which each LED will light with rising RPM but it prevents the last lit LED from extinguishing unless the RPM drops by the hysteresis RPM setting. The default hysteresis setting is 50 RPM and this can be altered in 1 RPM steps from 0-255 RPM. Note that the hysteresis value must be less than the RPM/LED value (see mode 4). Mode 8 – Digital Display Update Period: the LED bargraph is updated every 1ms but this is much too fast for the digital display to be read if there are any RPM changes. As a result, the digital display update is slowed down to a more comfortable rate. Typically, a 200ms update period (or five changes per second) is suitable. It can be altered from the default setting of 250ms in steps of 2 from 0-510ms. Mode 9 – Display Format: this adjustment is mainly to cater for engines that rev above 10,000 RPM. The initial setting of “0” sets the display to show RPM from 0-9999 RPM. Above this figure, the display shows a “0” for 10,000 RPM, “1000” for 11,000 RPM etc. Use this setting for engines that do not rev above 10,000 or which only occasionsiliconchip.com.au Fig.8: this diagram shows how to make the bracket and rear panel for the display housing, while the cross-section diagram at left shows how the display assembly goes together. ally rev to this RPM level. For engines that do rev above 10,000 RPM, a “1” or “2” setting will be best. The “1” setting shows the RPM with a shifting decimal point. Below 10,000 RPM the display will show, for example, 9.999 RPM (ie, 9999 RPM), while at 10,000 RPM and above the display decimal point will shift to the right and show the RPM using two digits for the 1000’s value. For example, at 10,000 RPM the display will show 10.00. siliconchip.com.au This is the rear panel (inside view) prior to mounting the PC board. Note the three nuts soldered around the periphery. November 2006  83 The PVC tubing is fitted with a neutral-tint filter and is secured to the PC board and rear panel assembly using three Nylon screws. A black display mask made from film ensures that only the LEDs are visible. If you don’t want the shifting decimal point, select “2”. This will fix the decimal point for two 1000’s digits so, for example, 9999 RPM will be displayed as 9.99, while 10,000 RPM will be displayed as 10.00. Note that for a “2” setting, resolution is reduced to 10 RPM (ie, there’s no units digit). Similarly, for a “1” setting, the resolution is reduced to 10 RPM for RPM values above 9999. Mode 10 – Resolution: in some cases, displaying the RPM to 1 RPM resolution will only be a distraction since the engine may never be stable enough to keep this digit steady – even at a constant throttle. In this case, you can select a “1” for this mode so that the far righthand digit always shows a zero (ie, the resolution is reduced to 10 RPM). Note that this won’t change the display for a “2” setting in Mode 8, because the units digit is not shown. Alternatively, selecting “10” in this mode sets both the units and tens digits to 0. The resolution for the digital display will then be 100 RPM. Mode 11 – Dot or Bargraph: you use this mode to select whether the LED bargraph operates in dot mode (ie, one 84  Silicon Chip You will have to drill and cut suitable holes in the rear panel to accept the power supply and input signal wiring and the IDC cable header. LED lit at any time) or as a continuous bargraph. Select a “0” for dot mode or a “1” for continuous bargraph mode. Mode 12 – Limiter Sense: this mode selects the output sense of the limiter. If “0” is set, the limiter output is normally at 0V and goes to +5V when the RPM rises above the limit setting. Conversely, if “1” is set, the limiter output is normally at +5V and goes to 0V when the limit setting (set in Mode 6) is reached. siliconchip.com.au Connecting A Rev Limiter To The LED Tachometer The limiter output from the tacho­ meter can optionally be used to drive a separate circuit that limits the maximum engine RPM. You can either use an ignition control circuit to do this or a fuel control circuit. Let’s take a closer look at both these options. (1) Ignition Control Limiting An ignition limiter control was published in SILICON CHIP for April 1999. Called a “Rev Limiter”, it’s suitable for use with cars that have a single ignition coil. When the rev limit is reached, the tachometer’s limit output activates the engine limiter, which then acts to reduce the number of sparks per revolution. Note that you don’t have to use the whole circuit from the Rev Limiter. Instead, you only have to use the Ignition Switcher circuit that was assembled on the separate PC board. This Ignition Switcher uses a single 555 timer IC and several transistors to drive a high-voltage Darlington output transistor. When the rev limit is reached, this transistor shunts out the main switching transistor in the car’s ignition system for about 50% of time, thus reducing the engine power and thereby limiting the engine RPM to the red-line. The two circuits are easy to marry – all you have to do is connect the limit output from the LED Tachometer directly to the terminal marked “From Rev Limit Controller” on the Ignition Switcher. A suitable value for C1 must be chosen for the Ignition Switcher from the table published in the April 1999 issue. This sets the requisite Mode 13 – Limiter On Period: this sets the minimum period that the limiter output is active in order to reduce engine RPM to a point below the limit setting. We suggest experimenting with the on periods at a low RPM limit setting and then altering the RPM limit (in Mode 6) to its final value afterwards. OK, that completes the setting up siliconchip.com.au Fig.9: here’s how to wire the tachometer to the DC Relay Switch board to provide fuel-cut limiting of engine RPM. number of sparks that are blocked out during the limiting action. Note that if the LED Tachometer derives its input signal from the coil, it will sense that the RPM has dropped as soon as the coil is prevented from “sparking” via the limiter action. This means that the limit action may not be as smooth as it would be if the tachometer signal were derived from a different source, such as the tacho­ meter output from the ECU. The limit output from the tachometer will remain low to disable the spark for the period that you select. A value of 300ms should provide sufficient time for the limit action to take place. Note that you must set the tachometer’s limiter sense to a “1”, so that the limiter output is normally at 5V and goes to 0V at the limit point. (2) Fuel Cut-Out Limiting A suitable fuel cut-out circuit is published elsewhere in this issue of SILICON CHIP. It’s called a “DC Relay Switch” and it can be used with the procedure. Now let’s complete the construction Tachometer housing If you have an old car, you may be able to install the display board within the existing instrument cluster. Depending on the car, it could either be fitted into a blank space or used tachometer’s limit output to switch off the supply to the fuel injectors. Note that it is suitable only for cars with injectors that are electrically driven (as used in most cars). The tacho’s limiter output drives the relay board as shown in Fig.9. When the red-line limit is reached, the normally closed (NC) relay contacts open and interrupt the positive supply rail to the fuel injectors. The unit is easy to install – just break the +12V supply lead to the injectors and connect the supply side to the relay’s COM (common) terminal. The NC (normally closed) contact is then connected to the injectors. Note that you must set the tacho­meter’s limiter sense to “0” (in Mode 12), so that the limiter output is normally at 0V but goes to +5V at the limit point. You may need to experiment with the limiter on period (set up in Mode 13) for best results. Start with a period of 100ms and decrease or increase this value until you are happy with the limiter action. to replace an unused instrument (eg, a clock). Alternatively, the display board can be built into a small cylindrical housing (see photos). This can be mounted inside the car by attaching it to the windscreen using a suction cap, or it can be fastened to the dashboard via a custom mounting bracket. November 2006  85 Fig.10: the LED Tachometer can derive its input signal from a variety of trigger sources, as shown here. In most modern cars, you will be able to use the tachometer output signal from the engine control unit (ECU). A suitable housing can be made using a 90mm-diameter PVC pipe cut to a length of 21mm. In addition, you will need a 90mm-diameter galvanisedsteel plate for the rear panel and this should be cut and drilled as shown in Fig.8. Three M3 nuts are then soldered around the circumference of this disc in the locations shown. Having done that, carefully mark out and drill three 3mm-diameter countersink in the PVC tube, to exactly line up with these nuts. These holes must also be positioned 5mm in from the rear edge of the tube and should all be countersunk using a slightly oversize drill. Be sure to accurately position these holes around the circumference of the PVC tube, so that they line up with the nuts on the rear plate. The IDC cable passes through a slot in the edge of the plate. This is made by making two cuts and then folding the edge over to as shown in one of the photos. That done, fit four M3 x 6mm-long tapped Nylon spacers to the four inner 86  Silicon Chip holes marked “X” on Fig.8 and secure them using M3 x 12mm Nylon screws. The PC board can then be mounted on these spacers and secured using Nylon nuts. The next job is to make up the aluminium bracket shown in Fig.8. This bracket is attached to the rear plate using M3 Nylon screws, nuts and washers and is fitted with a suction cap to secure the display to the windscreen. You will have to bend the bracket by 20-30° before attaching it to the end plate, to compensate for the rake of the windscreen. Note that it may also be necessary to fit a Nylon washer between the bracket and the rear panel at each mounting point, so that the bracket clears the rear lip of the PVC tube. Alternatively, you can fashion a suitable bracket to attach the display to the dashboard. All that remains now is the final assembly. The cross-sectional diagram in Fig.8 shows how it all goes together. As with the rear plate, the neutraltint front display filter is also 90mm in diameter and should be a tight fit into the PVC tube, so that it stays in place. Apply a couple of small blobs of silicone sealant to the inside rim to secure it in place if it’s a loose fit. If necessary, a black display mask (made from film) can be used to blank out all but the LED displays, so that the PC board and other components cannot be seen through the filter. This will most likely be included in any kits supplied by retailers but if not, you can download the artwork file from the SILICON CHIP website and print it out on clear film. Finally, the PC board and plate assembly can be pushed into the PVC tube and secured using three M3 x 12mm countersink Nylon screws. Installation The first job here is to mount the control box in a suitable location. This needs to go somewhere under the dashboard in a car or inside the side panels of a motorcycle (use silicone sealant to waterproof the cases). Power for the unit can be derived siliconchip.com.au Want cheap, really bright LEDs? We have the best value, brightest LEDs available in Australia! Check these out: Luxeon 1, 3 and 5 watt All colours available, with or without attached optics, as low as $10 each Low-cost 1 watt Like the Luxeons, but much lower cost. •Red, amber, green, blue and white: Just $6 each! Lumileds Superflux These are 7.6mm square and can be driven at up to 50mA continuously. •Red and amber: $2 each •Blue, green and cyan: $3 each Asian Superflux Same as above, but much lower cost. •Red and amber: Just 50 cents each! •Blue, green, aqua and white: $1 each. The IDC cable emerges from the display unit via a 15mmwide slot in the rear panel. At top right is a close-up view of the bracket and suction-cup assembly which allows the unit to be easily attached to a car’s windscreen. from an ignition-switched +12V supply, along with an earth (ie, chassis) connection. In most cars, you will be able to make the +12V connection at the fusebox. Connect to the fused side of the switched +12V supply and use automotive cable and crimp connectors to make the connections. Depending on the car, the input signal for the tachometer can be obtained from the switched (negative) side of the ignition coil primary, from a reluctor or from a tachometer signal provided by the engine control unit (ECU). It’s also possible to use the signals from a Hall effect trigger and from optical triggers. Fig.10 shows all the options. In most modern cars, you can use the ECU’s tachometer signal (C), in which case the link on the control board should be fitted to the LK2 position (ie, to select a low-level input). The link should also go in the LK2 position if you are deriving the signal siliconchip.com.au from a Hall effect sensor (E) or from an optical pick-up (F & G). Alternatively, fit the link in the LK1 (high-level signal) position selection if the signal is derived from the switched side of the ignition coil (A or B). This selection should also be suitable for most reluctors (D). Note that you will need to experiment to determine which lead to use for a reluctor. A reluctor has two leads and only one will have a signal that’s suitable for driving the tachometer. If the tachometer only operates at higher revs and stays at 0 RPM at lower revs, then the reluctor signal level may not be high enough for reliable triggering. In this case, change the link to the LK2 position. Note also that if the tachometer’s reading is erratic when connected to an ignition coil, try adding the second 47nF capacitor. In stubborn cases, this 47nF capacitor may need to be SC increased to 100nF. Go to www.ata.org.au or call us on (03)9419 2440. Serial-to-TCP/IP Converters from TRUSYS Trusys BF-430 & BF-450 universal serial device servers allow your industrial serial devices – such as PLCs, flow meters, gas meters, CNC machines and biometric identification card readers – to be monitored from your network. They support web management & firmware upgrade, while PPPoE & DDNS protocol allows Internet connection without static IP. 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